Field of the Invention
This invention relates to a rolling method making use of an edger in a heavy plate rolling process, and particularly to the rough rolling step in a hot strip rolling process, a blooming process or the like, a continuous hot rolling mill, and a variable caliber type edger roll.
Description of the Prior Art
In the course of the rough rolling in the above-mentioned hot strip rolling process for example, each stock material to be rolled (hereinafter called "stock material" for the sake of brevity) is rolled down to such a thickness that it can be rolled further by its subsequent continuous finishing mill and at the same time, it is also subjected to edge rolling so as to obtain a rolled product having a prescribed width. When effecting the edge rolling by means of a pair of cylindrical vertical rolls as a vertical scale breaker (VSB) or edger in the above width-adjusting rolling, namely, edger-rolling, applications of rolling forces to stock materials often tend to cause the stock materials to ascend at one side thereof where they are in contact with vertical rolls. Accordingly, it is impossible to perform sufficient widthwise rolling, leading to reduced widthwise dimensional accuracy. Furthermore, such an ascent results in the formation of a stepped portion in the corresponding side face of the rolled material, leading to reduced perpendicularity. Thus, such an ascent results in a reduction in production yield. If the above-mentioned one-side ascent phenomenon takes place on a stock material, the ascent side is alternated from the working side to the drive side and vice versa from one pass to another in an edge-rolling pass. This will increasingly reduce the widthwise dimensional accuracy of the stock material and will also promote the deterioration of its end profile. These phenomena are also developed in much the same way in a heavy plate rolling process or in the edger rolling of a blooming process.
A variety of edger rolling methods have heretofore been proposed with a view toward overcoming the above-mentioned problems. For example, a representative method of such conventionally-proposed edger rolling methods to employ tapered rolls having upwardly increasing diameters as vertical rolls or to arrange cylindrical vertical rolls in a fashion tilted widthwise (see, Japanese Patent Laid-open No. 116259/1978) so that a holding force is produced against a stock material to avoid bucking or ascent thereof upon its rolling. However, such mehtods are still unable to achieve any complete prevention of ascent. Conversely, such may in some instances affect adversely on the buckling. In addition, the perpendicularity of the side edge faces of stock materials may be reduced by tapered vertical rolls or widthwise inclination of vertical rolls.
It has also been proposed to provide a holding roll to depress a central part of a stock material. Although such a holding roll appears to be effective for the prevention of bucking or ascent, it requires the rolling mill to be unavoidably complex and its maintenance and servicing thereof difficult. If a stock material is warped upwardly, the stock material strikes the holding roll. This collision of the stock material not only damages equipment but also hinders smooth operation. In addition, it has also been proposed to conduct rolling by using caliber rolls as vertical rolls (see, Japanese Patent Publication No. 7322/1980). Basically speaking, use of such caliber rolls is however intended to achieve considerable widthwise rolling reduction while minimizing the problem of insufficient bite and occurrence of slippage. Caliber rolls are thus accompanied by a drawback in that they cannot prevent the ascent phenomenon where plate thicknesses are smaller than caliber dimensions. The above-described conventional various edger rolling methods are therefore believed to be extremely insufficient for the prevention of the buckling phenomenon and ascent phenomenon. Under the circumstances, there does not appear to be any specific means effective, especially for the prevention of the one-side ascent phenomenon.
With the foregoing in view, the present inventors analyzed the one-side ascent phenomenon of stock materials upon rolling the same by edgers and also conducted many experiments on plasticine models making use of experimental rolling mills. As a result of various analyses, it has been found that the one-side ascent phenomenon of stock materials upon their rolling by edgers are caused principally for the following reasons:
(1) non-uniformity in profile of a stock material at its side edges;
(2) widthwise tilting of a stock material due to widthwise inclination of a roller table adapted to convey the stock material; and
(3) tilted arrangement of vertical rolls of an edger.
Among the above-mentioned causes, causes (2) and (3) may be removed by making improvements in the rolling facilities. Thus, it is possible to solve the one-side ascent phenomenon of stock materials by the thus-improved rolling facilities. With respect to the one-side ascent phenomenon induced by the profile of a stock material, it is necessary to know in detail the behavior of the stock material which behavior is attributed to the profiles of the side edges of the stock material upon its rolling.
Reference is now made to FIG. 1 which illustrates the cross-sectional profiles of stock materials schematically. As depicted in FIG. 1, stock materials may be classified into (a) stock materials (slabs) having deformed rectangularity or squareness in their widthwise cross-sectional profiles, (b) stock materials having asymmetric bulges formed upon their thickness-adjusting rolling (horizontal pass), and (c) stock materials having deformed or rolled diagonal corner portions. When rolling stock materials of these profiles by edgers, their materials are caused to flow due to plastic deformation of the stock materials induced by their widthwise rolling reduction. In each of the cross-sectional profiles of stock materials, the thicknesswise component of the flow of the material becomes greater, as shown in the drawing, at the corner portions A,A which are more protruded than the corner portions B,B. Accordingly, greater counter reactions are given against the material flow at the corner portions A,A by vertical rolls and the counter reactions produced against the material flow at the corner portions A,A and the corner portions B,B act as a couple force, thereby rotating the stock material. As a result, the stock materials are rotated in directions shown respectively by arrows in the drawing or, in other words, the stock materials are caused to develop one-side ascent.
As mentioned above, the causes (2) and (3) for the one-side ascent phenomenon may be successfully removed by making improvements in the rolling facilities. As trains of rough rolling mills suitable for use in the hot strip rolling process, there are known (1) the semi-continuous type, (2) the fully-continuous type, (3) the three quarter type, and so on. Whichever type is employed, a stock material S often develops as shown in FIG. 2 an upward bending deformation when exerted with a rolling force F by a pair of vertical rolls 1 upon the width-adjusting rolling in the course of its rough rolling. Accordingly, the stock material is rolled at its edge portions and deformation does not take place evenly in the widthwise direction of the stock material S. If the above-mentioned upward bending deformation should occur to an extreme degree, the width-adjusting rolling cannot be effected any further due to the buckling phenomenon of the stock material S. The buckling phenomenon is generally called "buckling". Accordingly, the width-adjusting rolling in the hot strip rolling process has heretofore been believed to be on the order of 50-60 mm or so at most.
It is to be further noted that the continuous casting technique has been finding more and more utility in recent years from the viewpoint of placing more importance on economy. It has also been attempted in various ways to combine continuous casting facilities with various steps of the hot strip rolling process and to thus achieve still further energy reduction and still higher productivity by subjecting continuously- cast slabs to hot charge rolling or direct shipment rolling, i.e., hot strip rolling. Since there is however a limitation imposed on the widthwise reduction rate in rough rolling as mentioned above, widthwise rolling passes are limited in trains of rough rolling mills of the above-mentioned types, especially when the fully-continuous type is employed. Accordingly, the above limitation acts to to a reduced production yield. It is also necessary to provide as continuously-cast slabs those having various dimensions conforming with the dimensions of final products so that the edger rolling, which constitutes the rear stage of the three quarter type, can be performed without failure to roll the widths of products with good accuracy. However, production of such slabs results in a reduction in the rate of operation of continuous casting facilities. Such also inhibits the above-mentioned continuation of the continuous casting step and hot strip rolling step. If an edger rolling method capable of providing a large widthwise rolling reduction can be applied to the rough rolling step in the hot strip rolling process, it is possible to conduct the widthwise rolling reduction successfully by means of a train of rough rolling mills. This enables setting slab dimensions, in other words, the widthwise dimensions of slabs in the aforementioned continuous casting facilities at some representative values. Therefore, it is possible to cut down the preparatory time required to change molds in accordance with changes in widthwise dimensions, thereby improving the rate of operation of continuous casting facilities. It is also feasible to combine the continuous casting step and the hot strip rolling step together into a continuous process.
It is a normal practice to conduct rolling by means of caliber rolls with a view toward achieving large widthwise rolling reductions upon rolling widthwise by the above-described vertical scale breakers or vertical roll. It is necessary to change the dimensions of the above-mentioned calibers as the thickness of each stock material varies in various ways. In order to have calibers follow variations in thickness dimensions of stock materials, edger rolls capable of changing their caliber dimensions have been proposed for example in Japanese Utility Model Publication No. 1881/1977. In each of such edger rolls, a sliding portion of one of its movable flange portions which constitute a caliber is worn out after its application over a prolonged period of time, thereby forming a gap in the sliding portion. Accordingly, a stock material may be bitten in the gap or the resulting sliding corner portion of the movable flange portion may leave press marks in the corresponding side edge of a stock material, resulting in defective products. In addition, a stock material undergoes the one-side ascent phenomenon or the like especially when an excessive rolling load is applied to the stock material upon its rolling by such edger rolls or the profiles of the side edges of the stock material are not uniform vertically. The one-side ascent phenomenon or the like then exerts a tremendous rolling counter force to the caliber adjustment mechanism. Accordingly, the above-mentioned caliber rolls are accompanied by a drawback that their caliber mechanisms become unavoidably complex if one wants to protect them from such tremendous rolling counter forces.